192 Scientific Proceedings, Royal Dublin Society. 
change in the composition of the air with the clearing off of a 
fog, is also of interest :— 
Date COs i taoe Vales | UG ee 
October 26, 1882. 9-9 5:0 (2 hours after). 
November 18, 1882. 9-6 BO GE 95 set Ne 
December 1, 1882. 5:5 4:1 (44 ,, Rene 
December 20, 1882. 81 5:2 (1F ,, op! ie 
October 11, 1883. 76 PIL (GH - o¢ mama 
April 27, 1884. 5:3 4-6.(20 15. ee 
In both London and Manchester fogs the conditions may be 
said to be artificial, and, no doubt, the combustion of coal is mainly 
responsible for the very high proportion of carbonic anhydride. 
But Reiset proved that even in country districts a marked increase 
occurs during misty and foggy weather. ‘“ ‘Twelve experiments,” 
he says, ‘“‘made under these conditions, in 1879, have given a 
mean of 3:166. In 1880 (mean of five experiments), 3°2383! 
during calm nights with fogs or mists. . . . One remarks, with 
interest, that in series 2 of the determinations the absolute maxi- 
mum 3°415, on the 3rd of September, was succeeded, after twenty- 
four hours of an interval, by a minimum of 2°7438, obtained on a 
bright sunshiny day. An intense fog, with northerly wind, had 
brought about this sudden perturbation in the proportion of the 
carbonic gas.” His explanation of the cause is as follows :— 
“The vesicular vapour which constitutes fog can without doubt 
condense a small proportion of carbonic anhydride in a deter- 
minate volume of air; but I have not been able to establish any 
relationship between the hygrometric condition of the air and the 
proportion of carbonic acid. It would be more rational, perhaps, 
to admit, that during the calm which accompanies fog, the air, 
which so to speak is confined, is submitted to the direct influence 
of emanations from the earth, and of phenomena due to the 
1 The mean amount of atmospheric carbonic anhydride found by him, in 1879-1880, 
at Dieppe, was 2°985. 
